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          JavaScript基础数据结构
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<h1 id="数组"><a href="#数组" class="headerlink" title="数组"></a>数组</h1><h2 id="数组可以用来存储不同类型的变量"><a href="#数组可以用来存储不同类型的变量" class="headerlink" title="数组可以用来存储不同类型的变量"></a>数组可以用来存储不同类型的变量</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> simpleArray = [<span class="string">'one'</span>, <span class="number">2</span>, <span class="string">'three'</span>, <span class="literal">true</span>, <span class="literal">false</span>, <span class="literal">undefined</span>, <span class="literal">null</span>]</span><br></pre></td></tr></table></figure>

<h2 id="数组常用的几个方法"><a href="#数组常用的几个方法" class="headerlink" title="数组常用的几个方法"></a>数组常用的几个方法</h2><ul>
<li>删除（pop、shift），添加（push、unshift），slice，splice</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]</span><br><span class="line"><span class="comment">// push 向数组末尾插入一个值</span></span><br><span class="line">arr.push(<span class="number">1</span>)</span><br><span class="line">log(arr) <span class="comment">//[ 1, 2, 3, 4, 5, 1 ]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// // pop 在数组末尾删除一个值</span></span><br><span class="line">arr.pop()</span><br><span class="line">log(arr) <span class="comment">//[ 1, 2, 3, 4, 5 ]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// // shift 在数组开头删除一个值</span></span><br><span class="line">arr.shift()</span><br><span class="line">log(arr) <span class="comment">//[2, 3, 4, 5 ]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// // unshift 向数组开头插入一个值</span></span><br><span class="line">arr.unshift(<span class="number">1</span>)</span><br><span class="line">log(arr) <span class="comment">//[ 1, 2, 3, 4, 5 ]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// slice </span></span><br><span class="line"><span class="comment">// 1.slice只有两个参数，第一个参数接收数组索引的开头，第二个参数接收数组索引的结尾，但是不包括结尾的值</span></span><br><span class="line"><span class="comment">// 2.slice不会修改数组，而是会复制</span></span><br><span class="line"><span class="keyword">let</span> arrSlice = arr.slice(<span class="number">1</span>, <span class="number">3</span>)</span><br><span class="line">log(arr) <span class="comment">//[ 1, 2, 3, 4, 5 ]</span></span><br><span class="line">log(arrSlice) <span class="comment">//[ 2, 3 ]</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// splice</span></span><br><span class="line"><span class="comment">// 1.splice有两个功能，删除和添加</span></span><br><span class="line"><span class="comment">// 2.删除</span></span><br><span class="line"><span class="comment">// 2.1.可以接收三个参数</span></span><br><span class="line"><span class="comment">// 2.2.第一个参数是索引，即开始的地方；第二个参数是要删除的数量</span></span><br><span class="line">arr.splice(<span class="number">1</span>, <span class="number">2</span>)</span><br><span class="line">log(arr) <span class="comment">//[ 1, 4, 5 ]</span></span><br><span class="line"><span class="comment">// 3.添加</span></span><br><span class="line"><span class="comment">// 3.1.第三个参数可以将连续的值插入到删除的项的地方</span></span><br><span class="line">arr.splice(<span class="number">1</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>)</span><br><span class="line">log(arr) <span class="comment">//[ 1, 2, 3, 4, 5 ]</span></span><br></pre></td></tr></table></figure>

<h2 id="展开运算符"><a href="#展开运算符" class="headerlink" title="展开运算符"></a>展开运算符</h2><ul>
<li>复制数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]</span><br><span class="line"><span class="keyword">let</span> arrCopy = [...arr]</span><br><span class="line">log(arrCopy) <span class="comment">//[1, 2, 3]</span></span><br></pre></td></tr></table></figure>

<ul>
<li>合并数组</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> h=[<span class="string">'hello'</span>,<span class="string">'hello'</span>]</span><br><span class="line"><span class="keyword">let</span> w=[<span class="string">'world'</span>,<span class="string">'world'</span>]</span><br><span class="line"><span class="keyword">let</span> hw=[...h,...w,<span class="string">'!'</span>] <span class="comment">//[ 'hello', 'hello', 'world', 'world', '!' ]</span></span><br></pre></td></tr></table></figure>

<h2 id="indexOf"><a href="#indexOf" class="headerlink" title="indexOf"></a>indexOf</h2><p>***indexOf 的意义在于：由于数组随时都可以修改或发生 mutated（突变），我们很难保证某个数据始终处于数组中的特定位置，甚至不能保证该元素是否还存在于该数组中。所以 indexOf 可以用来检测以上问题</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// indexOf 接收一个元素作为输入参数，如果目标数组中存在，则返回其存在位置的索引，反之返回-1</span></span><br><span class="line"><span class="keyword">let</span> arr = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>, <span class="number">5</span>]</span><br><span class="line">log(arr.indexOf(<span class="number">3</span>)) <span class="comment">//2</span></span><br><span class="line">log(arr.indexOf(<span class="number">0</span>)) <span class="comment">//-1</span></span><br></pre></td></tr></table></figure>

<h2 id="for循环遍历数组"><a href="#for循环遍历数组" class="headerlink" title="for循环遍历数组"></a>for循环遍历数组</h2><ul>
<li>JavaScript 中实际上有多个遍历数组的方法，如 every()、forEach()、map()。但是简单的 for 循环就能实现他们的功能，并且也更加灵活。</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * </span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param <span class="type">&#123;Array&#125;</span> </span>arr </span></span><br><span class="line"><span class="comment"> * <span class="doctag">@param <span class="type">&#123;Number&#125;</span> </span>elem </span></span><br><span class="line"><span class="comment"> * <span class="doctag">@returns <span class="variable">newArr</span></span></span></span><br><span class="line"><span class="comment"> * <span class="doctag">@description </span>判断arr中是否含有elem，如果没有则将arr中没有elem的项存储在newArr中并return</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="function"><span class="keyword">function</span> <span class="title">filteredArray</span>(<span class="params">arr, elem</span>) </span>&#123;</span><br><span class="line">	<span class="keyword">let</span> newArr = []</span><br><span class="line">	<span class="keyword">for</span> (<span class="keyword">let</span> i = <span class="number">0</span>; i &lt; arr.length; i++) &#123;</span><br><span class="line">		<span class="keyword">if</span> (arr[i].indexOf(elem) === <span class="number">-1</span>) newArr.push(arr[i])</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="keyword">return</span> newArr</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="built_in">console</span>.log(filteredArray([[<span class="number">3</span>, <span class="number">2</span>, <span class="number">3</span>], [<span class="number">1</span>, <span class="number">6</span>, <span class="number">3</span>], [<span class="number">3</span>, <span class="number">13</span>, <span class="number">26</span>], [<span class="number">19</span>, <span class="number">3</span>, <span class="number">9</span>]], <span class="number">9</span>))</span><br></pre></td></tr></table></figure>

<h1 id="对象"><a href="#对象" class="headerlink" title="对象"></a>对象</h1><pre><code>对象的本质是一种键值对所组合而成的数据结构</code></pre><h2 id="delete-删除对象属性"><a href="#delete-删除对象属性" class="headerlink" title="delete 删除对象属性"></a>delete 删除对象属性</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">	x: <span class="number">1</span>,</span><br><span class="line">	y: <span class="number">2</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">delete</span> obj.x</span><br><span class="line">log(obj) <span class="comment">//&#123; y: 2 &#125;</span></span><br></pre></td></tr></table></figure>

<h2 id="检查对象是否具有某个属性"><a href="#检查对象是否具有某个属性" class="headerlink" title="检查对象是否具有某个属性"></a>检查对象是否具有某个属性</h2><p>*JavaScript 总共有两种方法可以检测对象中是否含有某种值：hasOwnProperty()、关键字 in</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">	x: <span class="number">1</span>,</span><br><span class="line">	y: <span class="number">2</span></span><br><span class="line">&#125;</span><br><span class="line">log(obj.hasOwnProperty(<span class="string">'x'</span>)) <span class="comment">//true</span></span><br><span class="line">log(<span class="string">'x'</span> <span class="keyword">in</span> obj) <span class="comment">//true</span></span><br></pre></td></tr></table></figure>

<h2 id="使用-for…in-语句遍历对象"><a href="#使用-for…in-语句遍历对象" class="headerlink" title="使用 for…in 语句遍历对象"></a>使用 for…in 语句遍历对象</h2><figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">	Alan: &#123;</span><br><span class="line">		online: <span class="literal">false</span></span><br><span class="line">	&#125;,</span><br><span class="line">	Jeff: &#123;</span><br><span class="line">		online: <span class="literal">true</span></span><br><span class="line">	&#125;,</span><br><span class="line">	Sarah: &#123;</span><br><span class="line">		online: <span class="literal">false</span></span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i <span class="keyword">in</span> obj) &#123;</span><br><span class="line">	log(i) <span class="comment">// 分别打印三个属性，要注意，打印出来的是 string 而不是 object</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>还有一个难点，如果是嵌套对象，想要通过 for…in 遍历访问内部值怎么办呢？还是用上面的对象</p>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">for</span> (<span class="keyword">let</span> i <span class="keyword">in</span> obj) &#123;</span><br><span class="line">	log(obj.i) <span class="comment">// 会打印出三个 undefined</span></span><br><span class="line">	log(obj[i]) <span class="comment">//应当用中括号形式去访问</span></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p>方括号里一定要是变量，而不是具体的值。比如上面的 i 就是定义的一个变量，所以必须要用中括号形式去表达！</p>
<h2 id="生成由对象的所有属性组成的数组"><a href="#生成由对象的所有属性组成的数组" class="headerlink" title="生成由对象的所有属性组成的数组"></a>生成由对象的所有属性组成的数组</h2><ul>
<li>使用 Object.keys()</li>
</ul>
<figure class="highlight js"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">	Alan: &#123;</span><br><span class="line">		online: <span class="literal">false</span></span><br><span class="line">	&#125;,</span><br><span class="line">	Jeff: &#123;</span><br><span class="line">		online: <span class="literal">true</span></span><br><span class="line">	&#125;,</span><br><span class="line">	Sarah: &#123;</span><br><span class="line">		online: <span class="literal">false</span></span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br><span class="line">log(<span class="built_in">Object</span>.keys(obj)) <span class="comment">//[ 'Alan', 'Jeff', 'Sarah' ]</span></span><br></pre></td></tr></table></figure>



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